Survey differences of the full-mission ((S1 + S3) − (S2 + S4)) maps in I, Q, and U (in columns) for the 2015 data (top panels) and the 2018 data (bottom panels). There are large improvements at CMB frequencies in the residuals for the 2018 data compared to those in the 2015 data. Bands are visible in the 353 GHz and 545 GHz intensity maps, due to the incomplete correction of the transfer function.